1. Field of the Invention
The present invention relates to a pressure sensor. More specifically, it relates to a pressure sensor having a small volume of pressure port into which a pressure of a fluid is introduced to improve a response of the pressure sensor in detecting the pressure.
2. Description of Related Art
A pressure sensor which detects a pressure difference between a detecting pressure and atmospheric pressure and converts the detected pressure difference into an electric signal is used for measuring fluid pressure.
The pressure sensor has a fitting attached to a fluid channel, a pressure detecting module attached to the fitting by welding etc. and an output device electrically connected to the pressure detecting module. A fluid pressure introduced into a pressure port of the fitting is converted into a strain of a diaphragm which forms the pressure detecting module, the strain is detected by a strain gauge on the diaphragm and an electric signal in accordance with the resistance value of the strain gauge is output by the output device.
The pressure port in the fitting of the pressure sensor, for installing in an automobile for example, is approximately 20 mm length and approximately 2.5 mm in diameter (length: diameter=approximately 8:1) according to the smallest model, and the pressure port is processed by a twist drill.
The pressure port of the pressure sensor is preferably small in diameter to reduce inner volume thereof so that a response of the pressure detecting module is improved. However, it has been difficult to further lessen the diameter of the pressure port and to reduce inner volume according to the conventional twist drill processing.
The object of the present invention is to provide a pressure sensor having small volume of a pressure port with a simple structure to enhance response thereof.
A pressure sensor according to the present invention has a fitting provided with a pressure port for introducing the fluid pressure and a pressure detecting module attached to the fitting and shutting an end of the pressure port. The pressure sensor is characterized in that a volume adjusting member having a penetrating channel of a smaller cross section than the pressure port is disposed inside the pressure port of the fitting.
As the volume adjusting member, a cylindrical member can be used for example. However, the volume adjusting member may be prism-shaped or shaped in other kind of block to be accommodated inside the pressure port to occupy inside of the pressure port at a volume corresponding thereto.
The penetrating channel may be a through-hole formed along a central axis of the cylindrical volume adjusting member. In this case, the through-hole naturally has smaller diameter than the pressure port.
On the other hand, the penetrating channel may be a groove cut into a side of the cylindrical volume adjusting member to reach both ends of the volume adjusting member. The groove may be formed in plural on a surface of the volume adjusting member, or may be cut on one part of the volume adjusting member to reach a central axis position (the cross section of the volume adjusting member is approximately C-shaped or U-shaped).
Alternatively, if the pressure port is a cylindrical space, inserting a prism-shaped volume adjusting member allows a predetermined aperture therearound. The aperture is naturally narrower than the pressure port, which can be used for introducing pressure.
According to the present invention, the volume adjusting member is preferably accommodated inside the pressure port so that the pressure is transmitted to the pressure sensor through the penetrating channel and the volume inside the pressure port is decreased by the volume of the volume adjusting member, thereby improving the response of the pressure sensor. Furthermore, a small diameter of the pressure port, which is difficult to be processed, is not necessary to be provided to the fitting by a twist drill, thereby facilitating manufacturing.
The pressure detecting module is preferably abutted and welded to the fitting, and the volume adjusting member is preferably disposed to a position corresponding to a welded part of the fitting and the pressure detecting module.
The position corresponding to the welded part refers to a position where the volume adjusting member covers the welded part from a back side thereof or the volume adjusting member extends over the welded part.
Accordingly, the fitting and the pressure detecting module can be securely mounted by welding and an over-penetration in welding can be prevented since the volume adjusting member is disposed to the position corresponding to the welded part of the fitting and the pressure detecting module so that the volume adjusting member works as a backing member in welding.
In conducting the welding, the abutting portion of the fitting and the pressure detecting module preferably has a tapered surface (a surface approximately conic) where the pressure detecting module is projected to grow narrower in proportion to a distance from the center of the pressure port, and the welding is preferably conducted from a direction of a slanting angle of the tapered surface.
Accordingly, since the abutting portion of the fitting and the pressure detecting module is tapered and the welding is conducted from the slanting angle direction of the tapered surface, welded area can be enlarged to further improve the bonding strength of the pressure detecting module, thereby allowing uses in a higher pressure range.
In welding (irrespective of being tapered or not), the welding direction is usually a central axis direction of the fitting and the pressure detecting module (radial direction).
On the other hand, the direction in which welding is conducted in the present invention is preferably offset in a predetermined direction relative to a central axis of the fitting and the pressure detecting module so that a trace of the welded part forms an envelope ranging sequentially with each other. More specifically, by arranging the weld trace for each part to align in a tangential direction along the side of the volume adjusting member, such envelope can be formed.
Accordingly, the welded area can be further increased, and over-penetration possibility can be decreased since the weld length of each part is made longer. Furthermore, irregularities caused inside can be made smaller as compared to welding in a radial direction.
The pressure detecting module of the present invention may have a cylindrical portion on a side connected to the fitting, and the volume adjusting member may be disposed to an end of the pressure port to which the pressure detecting module is attached with a part thereof being protruded, the outer side of the protruded part being a guiding surface contacted to the inner side of the cylindrical portion of the pressure detecting module.
Accordingly, since the pressure detecting module is guided by the outer surface of the volume adjusting member, the pressure detecting module can be easily disposed.
In the above, the volume adjusting member is preferably a cylindrical pipe obtained by drawing processing.
The response of pressure sensors is also largely influenced by a dimension accuracy of the through-hole. Accordingly, by producing the volume adjusting member with drawing processing, the dimension accuracy of the through-hole can be improved, thereby obtaining a pressure sensor stable in quality.